1. Field of the Invention
The present invention relates to biotechnology, and specifically to a method for producing an L-amino acid such as L-histidine, by fermentation. The present invention further relates to a gene derived from an Escherichia coli bacterium. The gene is useful for improving production of L-histidine.
2. Description of the Related Art
Conventionally, L-amino acids have been industrially produced by fermentation utilizing strains of microorganisms obtained from natural sources, or mutants of the same modified to enhance L-amino acid productivity.
Many techniques have been reported regarding enhancement of L-amino acid production, for example, by transformation of microorganism by recombinant DNA (see, for example, U.S. Pat. No. 4,278,765). These techniques are based on increasing of activities of enzymes involved in amino acid biosynthesis and/or desensitizing target enzymes from feedback inhibition by the produced L-amino acid (see, for example, Japanese Laid-open application No56-18596 (1981), WO 95/16042 or U.S. Pat. Nos. 5,661,012 and 6,040,160).
The talB gene encodes transaldolase (also known as TAL, or D-sedoheptulose-7-phosphate:D-glyceraldehyde-3-phosphate dihydroxyacetonetransferase) [EC 2.2.1.2], an enzyme of the non-oxidative pentose phosphate cycle (Sprenger G. A. et al, J. Bacteriol., 1995, October 177:20, 5930-6). Transaldolase is a key enzyme in biosynthesis of ribose-5-phosphate from glycolysis products. The enzyme catalyzes the reversible transfer of a dihydroacetone moiety derived from fructose-6-phosphate to erythrose-4-phosphate, forming sedoheptulose-7-phosphate and releasing glyceraldehyde-3-phosphate. Then sedoheptulose-7-phosphate and glyceraldehydes-3-phosphate are converted to two molecules of pentose-5-phosphate by the activity of transketolase.
Previously it has been reported that increasing the activity of transaldolase is useful for microbial production of substances from aromatic metabolism, in particular aromatic amino acids such as L-phenylalanine (U.S. Pat. No. 6,316,232).
Recently, it has been suggested based solely on theory that preparation of L-threonine by fermentation of microorganisms of the Enterobacteriaceae family, whereby one or more genes from a large group of genes, including the talB gene, are attenuated, in particular eliminated, can be accomplished. No experimental data, however, proving this theory was presented (WO03008600A2). At the same time, and in direct contradiction, preparation of L-threonine by fermentation of microorganisms of the Enterobacteriaceae family in which expression of at least talB gene is enhanced, in particular over-expressed, was disclosed WO03/008611A2).
There have been no reports to date, however, describing amplification of the talB gene for the purpose of enhancing L-histidine production using strains of the Enterobacteriaceae family.